Mercerization of cellulosic materials using a solution containing a mercerizing concentration of alkali and a barium compound

ABSTRACT

A minor amount of barium compound is incorporated in a mercerizing concentration of alkali to form a solution. A cellulosic material is treated with this solution to produce a high yield of mercerized product. This product contains a substantial amount of alkali-soluble, short-chain polysaccharides.

United States Patent lnventors Andrew Beelik Shelton; Jim D. Wilson,Olympia, both of Wash. Appl. No. 812,340 Filed Apr. 1,1969 Patented Nov.l6, 1971 Assignee International Telephone and Telegraph Corp. New York,N.Y.

MERCERIZA'I'ION OF CELLULOSIC MATERIALS USING A SOLUTION CONTAINING AMERCERIZING CONCENTRATION OF ALKALI AND A BARIUM COMPOUND 9 Claims, NoDrawings US. Cl 162/90, 8/ l 25 Int. Cl D2le 3/02 Field of Search 8/125;162/70, 90

Beelik et al., Selective Extraction of Hemicelluloses From Softwoods,"TAPPI Journal, Vol. 50, No. 2, February 1967, pgs. 78- 81.

Primary Examiner-S. Leon Bashore Assistant ExaminerArthur L. CorbinAttorneys-C. Cornell Remsen, Jr., Walter J. Baum, Percy P. Lantzy, J.Warren Whitesel, Delbert P. Warner and James B. Raden ABSTRACT: A minoramount of barium compound is incorporated in a mercerizing concentrationof alkali to form a solution. A cellulosic material is treated with thissolution to produce a high yield of mercerized product. This productcontains a substantial amount of alkali-soluble, short-chainpolysaccharides.

MERCERIZATION OF CELLULOSIC MATERIALS USING A SOLUTION CONTAINING AMERCERIZING CONCENTRATION OF ALKALI AND A BARIUM COMPOUND The presentinvention relates to new and improved mercerization methods and to theproducts prepared thereby. More particularly, it relates to methods forpreparing new and improved mercerized cellulose products containingsubstantial amounts of alkali-soluble, short-chain polysaccharides andto the products prepared thereby.

Throughout this specification, the term mercerization" is used to denotethe well-known treatment of cellulosic materials with aqueous solutionsof caustic alkalies. These caustic alkali solutions are concentratedsufficiently to cause extensive swelling of the cellulose andsubstantial changes in the physicalstructure of the cellulose. Among thechanged physical properties which are exhibited by cellulosic materialstreated in this manner are a reduction in density (increase in bulk) andincreased porosity.

Cellulosic materials exhibiting the above-described proper ties ofincreased bulk and porosity are very desirable for certain applications.For example, it is desirable for paper pulps to be utilized forimpregnation with elastomers in the manufacture of artificial leatherand the like to have these properties. Also, it is desirable for certainspecialty papers to exhibit these properties.

However, the mercerization treatment has certain inherent disadvantages.The swelling of the cellulose caused by mercerization increases theaccessibility of certain short-chain polysaccharides (hemicelluloses andlow D.P. celluloses) present in the native cellulose. Thus, heretofore,substantial amounts of these short-chain polysaccharides have beenremoved during mercerization. The removal of these constituents mayactually be advantageous in the production of certain types ofmercerized wood celluloses, such as dissolving pulps. However, theremoval of these short-chain polysaccharides is very undesirable inother instances.

For example, paper pulps are treated with mercerizing solutionsprimarily for the purpose of lowering density and increasing bulk. inthe production of these mercerized paper pulps. the removal ofhemicelluloses and low D.P. celluloses merely causes a highlyundesirable reduction in product yield Additionally, hemicellulosesgenerally improve the bonding properties of wood pulps. Consequently,the removal of the hemicelluloses during the mercerization treatmentcauses an undesirable reduction in the bonding qualities of the pulpfibers.

It would, therefore, be highly desirable and economically advantageousto provide a new and improved method for mercerizing cellulosicmaterials such as paper pulps which would allow for the retention of asubstantialpercentage of shortchain polysaccharides in the product. Theresulting product would also be of great value, for example, in theproduction of artificial leather and for specialty papers.

!t is, therefore, an object of the present invention to provide a newand improved method for mercerizing native cellulose whereinalkali-soluble, short-chain polysaccharides are retained in themercerized product.

Another object is to provide new and improved mercerized cellulosicproducts containing substantial amounts of alkalisoluble, short-chainpolysaccarides.

A further object is to provide a new and improved method for mercerizingnative cellulose whereby substantially in creased yields of mercerizedproduct are obtained.

Additional objects, if not specifically set forth herein, will beapparent to one skilled in the art from the following detaileddescription of the invention.

Generally, the method of the present invention comprises adding a minoramount of a barium compound such as barium hydroxide, barium chloride,barium acetate, barium sulfide and the like and mixtures thereof to astandard, aqueous alkali mercerizing solution such as sodium hydroxide,potassium hydroxide, lithium hydroxide and the like. This solution isthen employed to mercerize a cellulosic material such as bleached orunbleached wood pulp, cotton yarn or cloth and the like by known coldcaustic refining techniques.

In the cold caustic treatment of wood pulp and other types of cellulosicmaterials, mercerization normally starts at a caustic soda concentrationof about 5 to 7 percent at room temperature and will be substantiallycomplete at about 9 to l2 percent. Experience has shown that the mosteffective action is attained with from about 8 to l4 percent causticsoda present based on the weight of the solution. These percentages canbe raised and lowered somewhat by variations in origin of the and byvariations in temperature. Normally, mercerization increases with risingconcentration and decreases with rising temperature and vice versa.Therefore, as the temperature of the solution is raised the caustic sodaconcentration in the mercerizing solution must also be raised to obtainan equivalent effect on the cellulosic material being treated. On thewhole, however, the foregoing range holds very well for normal coldcaustic soda treatment presently employed.

Barium hydroxide has previously been employed in an experimentalprocedure for the selective extraction of hemicelluloses (e.g. TheJournal of the Technical Association of the Pulp and Paper Industry,Vol. 50, No. 2, Feb. 1967 article coauthored by one of the presentinventors). However, the purpose therein was to obtain separated andpurified hemicellulose fractions, and not the preparation of mercerizedcellulose products. Additionally, heretofore, it has been thought to beessential to preliminarily impregnate the cellulosic material withbarium hydroxide since the addition of the insolubilizing agent directlyto the extraction liquor gave inferior results.

More specifically, the present invention is based on our discovery thatthe single-step treatment of cellulosic materials with a solutioncomprising a minor amount of a barium compound such as barium hydroxide,barium chloride, barium acetate, barium sulfide and the like andmixtures thereof and a mercerizing concentration of alkali will providenew and improved mercerized products containing substantial amounts ofalkali-soluble, short-chain polysaccharides in substantially greateryields than have been achieved heretofore.

The concentration of barium compound to be incorporated into themercerizing solution has been found to be in the range of from about0.10 percent to about 3 percent based on the weight of the solution, andpreferably in the range of from about 0.5 percent to about 1.5 percent.However, it must be noted that the amount of barium compound to be usedin a given process will be dependent to a degree on the temperature ofthe solution and the concentration of caustic soda employed since thebarium compound solubility is sensitive to these two factors.

For example, at a solution temperature of 25 C. only about 0.6 percentbarium hydroxide will normally dissolve in a 9 percent aqueous sodiumhydroxide solution. Therefore, at this temperature and with thisconcentration of caustic soda it would not be practical on a productionscale to use levels greater than about 0.6 percent barium hydroxide;although, it would be possible to use higher concentrations of bariumhydroxide if the mercerizing solution was supersaturated with bariumhydroxide. At higher temperatures, of course, higher concentrations ofbarium hydroxide may practically be employed. In a pulp mill,mercerization is usually performed at about 3050 C. using about 9-l 1percent sodium hydroxide, under these conditions it would be feasible touse higher concentrations of barium hydroxide, e.g., 1.5 percent.

It has been found that the process of this invention may best be carriedout in a temperature range of from about 5 C. to about 60 C., in aaqueous caustic solution containing a minor amount of barium compoundand a mercerizing concentration of alkali. Preferably, the bariumcompound concentration in the caustic solution should be in the range offrom about 0.10 percent to about 3.0 percent by weight and the alkaliconcentration should be about 5-18 percent by weight.

the following examples are set forth for the purpose of illustrating themethod of this invention and the characteristics of the resultingproducts only and are not intended to be construed as being limitativein any respect.

EXAMPLE I taining L percent barium hydroxide and 9 percent sodiumhydroxide (solution basis). Since barium hydroxide absorbed atmosphericcarbon dioxide so readily that dissolution of the solid hydroxide inwater gave cloudy solutions containing precipitated barium carbonate,the barium hydroxide was added to the mercerizing solution, in each caseherein, as a near-saturated solution (about 3.5 percent) that had stooduntil all the precipitated barium carbonate had settled. The liquidcomponents were mixed together prior to treatment of the pulp.Mercerization was performed, as above at 25 C. Four more portions ofpulp were mercerized in the same manner as above except that the amountof barium hydroxide introduced into the mercerizing solution was variedin each case so that the solutions contained 0.75 percent, 0.5 percent,0.25 percent and 0.15 percent (solution basis) concentrations of bariumhydroxide respectively.

The yield of mercerized product was then determined for the portions andthe percentage yield on an ash-free basis was calculated. The percentageof increased yield was determined for the mercerized products preparedby treatment with barium hydroxide over the mercerized product which hadnot been treated with barium hydroxide.

Additionally, various standard tests were made on the foregoing pulpsamples after they had been treated as indicated. A determination wasmade of the S and S values of the samples by a method similar to TAPPIStandard T235m- 60. The S test determines the solubility of pulpproducts in DJ. 10 percent sodium hydroxide solution and gives anindication of the short-chain polysaccharide content (i.e., he-

micelluloses and low D.P. celluloses) of a pulp sample. The S testdetermines the solubility of pulp products in l8 percent sodiumhydroxide and gives an indication of the hemicellulose content of a pulpsample. Also, a determination was made of the mannan values of thesamples by the test procedures of Jeffery et al., Analytical Chemistry,32, 1774-7 (Dec., 1960). The mannan test is a measure of the predominanthemicelluloses (i.e. the glucommannans) present in the samples.

The results of this testing are tabulated in the following table:

cerized product. These increased yields result from the reduction in theamount of hemicellulose and low D.P. cellulose dissolved out of the pulpduring mercerization. The increased S S and mannan values for the pulpsmercerized with barium 5 hydroxide addition indicate this increasedretention of shortchain polysaccharides as compared with pulps treatedin the conventional manner.

EXAMPLE ll Another standard test was performed with each of the sevenportions of hemlock sulfite paper pulp preparation in example I. In thistest, a determination was made of the limit intrinsic viscosity or limitl.V.s" of each of the portions. This test af- 5 fords a sensitive andaccurate method for detecting mercerization since the limit l.V. of acellulosic material is sharply lowered by mercerization. Consequently,this test was conducted to determine the effect that the introduction ofbarium hydroxide into the mercerizing solution had on the themercerization of these pulp samples.

In determining the limit l.V. for these samples, 0.3 grams of the pulpwas osterized (ground to a fine particle size) and then hydrolyzed for35 minutes in 75 mls. of 2.0 N HCl at I00 C. The sample was thenfiltered, washed with water and methonal and dried at 1 15 C. THe limitl.V. was then determined by a standard method similar to that describedby the Scandanavian pulp paper and boardtesting committee SCAN-C 15:62.

The results of this testing are tabulated in the following table TABLEll Mercerizing Solution Limit l.V. NaOl-l% Ba(0l-l)2% 'dL/ 0.0 0.0 L 409.0 0.0 0.70 9.0 L0 080 9.0 0.75 0.83 9 0 0.50 0.87 9.0 0.25 0.86 9.00.l5 0.97

Limit l.V. is limit intrinsic viscosity in dccilitcrs/grlm (dl./g.).

From the foregoing results it is apparent that the addition of effect onthe mercerization of the product. Thus, it has been product (i.e. nobarium hydroxide treatment).

As indicated in the table above, conventional mercerization (i.e.,without barium hydroxide) was accompanied by a substantial loss of pulpand, consequently, a large reduction in yield of mercerized pulpproduct. This reduced yield can be attributed to the removal of thehemicelluloses and degraded or low D.P. cellulose as indicated by thesubstantial drop in S S and mannan values. The addition of bariumhydroxide was shown to reduce the loss of pulp during mercerization and,consequently, to substantially increase the yield of mer- Increase inyield expressed as percent increase over 88% yield of conventionallymercerized shown that the yield benefits derived from this inventionhave been accomplished without interfering with mercerization.

7O EXAMPLE III A supply of fully bleached, never dried southern pineconventional kraft pulp was divided into five separate portions. Theseportions were treated in the same manner as were the samples in exampleI. One portion was mercerized with 9 percent (solution basis) sodiumhydroxide at 25 C., and used as a control. The four other portions weretreated with previously prepared solutions each containing sodiumhydroxide and barium hydroxide at 25 C. The concentration of sodiumhydroxide in each of these four solutions was 9 percent (solutionbasis), while the concentran'on of barium hydroxide in the foursolutions was 1.5 percent, 1.0 percent, 0.75 percent and 0.5 percent(solution basis) respectively. These four solutions were prepared in thesame manner as the solutions of example I were prepared.

The yield of mercerized product was then determined for each of theportions and the percentage yield on an ash-free basis was calculated.The following table gives the results of this testing which clearlyshows the substantial increase in yield achieved by introducing bariumhydroxide into the mercerizing solution:

TABLE III Percent yield mercerized Increased Solution product yield overMercerizing Ba(OH);, (ash tree control, NaOH, percent percent basis)percent 1 Increase in yield expressed as a percent increase over the87.8 percent yield of the control.

1 Control.

EXAMPLE IV Each of the five mercerized portions of southern pineconventional kraft pulp prepared in example [ll were subjected to thelimit i.V. "test in the same manner as described in example 11. Anunmercerized sample of southern pine conventional kraft pulp wasintroduced into this testing as a sixth sample for the purpose ofproviding a standard for the limit I.V." test.

The results of this testing are tabulated in the following table:

' deciIiters/gram From the foregoing results it is apparent that theaddition of barium hydroxide to the mercerizing solution had very littleeffect on the mercerization of the product. Thus, it was shown that theyield benefits derived by the process of this invention have beenaccomplished without interfering with mercerization.

EXAMPLE V A supply of unbleached southern pine conventional kraft pulpof a type commonly processed into a commercial grade of mercerized paperpulp was bleached by a sequence including chlorination, washing, hotdilute caustic soda extraction, washing, chlorine dioxide treatment andwashing. This bleaching operation was carried out on a semiworks scaleto a degree such that the pulp was ready to be mercerized. The

properties of pulp treated in this manner are indicated in the followingtable (table V) under the heading Pulp Before Mercerization."

A sample of bleached southern pine conventional krafi pulp was thendivided into two discrete portions. One of the portions was mercerizedby conventional techniques. The other portion was mercerized in the samemanner except that barium hydroxide was added to the mercerizingsolution.

For mercerization with barium addition, the never dried pulp (7.7 kg.wet, 2.8 kg. dry basis) was added to a 40 C. mixture of water, aqueous3.5 percent barium hydroxide solution and 18.5 percent sodium hydroxidesolution to give a 3 percent consistency slurry in a solution containing9 percent sodium hydroxide and 1 percent barium hydroxide. The slurrywas maintained at 40 C. for 15 minutes, with constant agitation. Then,the slurry was transferred to a centrifuge and the liquor removed. Partof this liquor was used to wash any remaining pulp out of themercerizing tank. The unwashed pulp cake was then reslurried (2.0percent -2.5 percent consistency) in water-made acid with sulfur dioxide(ph 3) and agitated at room temperature for 10 minutes. it was thenrecentrifuged and washed with deionized water to give the finishedmercen'zed product.

The other portion of bleached pulp was mercerized in the same mannerexcept that that barium hydroxide was not included in the mercerizedsolution. This portion was employed as a control.

The following table gives the results of various standard tests made onthe foregoing pulp samples afier they had been treated as indicated andon sheets formed with this pulp. in order to form these test she sheets,the pulp samples were dried, reslurried and formed into sheets on aTAPPI sheet mold.

TABLE V Pulp mrrccr- Pulp mercerlulp before ized without ized withmercerization Bn(0 II); (011):

Yield:

Yield (percent) o 100. 0 89. 1 92. 5 Increased yield (percent) 0. 0 0. 03. 8 Pulp properties:

m (percent) 14. 7 3. 74 6. 72 Si; (percent) 13. 97 3. 48 5. 7! LimitI.V. (dl./g.). l. 51 0. 94 0. 92 Xylan (percent J. 1 1. 8 .2. 1 Mannan(percent) 7. 0 4. J 7. 2 Sheet properties:

Density (g./cm.) 0. 44 0.31 0. 35 Air permeability (c.l.m.) 20 98 73'Incrcase in yield expressed as a precent increase over the 80.1 percentyield of the control.

EXAMPLE VI A supply of partially bleached southern pine conventionalkraft pulp was divided into three equal portions. Each of the portionswas mercerized according to the general procedure of example 1 exceptthat the mercerizing temperature was raised to 40 C.

The first portion of pulp was mercerized by conventional means with 9percent sodium hydroxide as a control. The yield of mercerized pulpproduct obtained was 87.6 percent.

The second portion of pulp was mercerized in the same manner as thefirst except that barium chloride (equivalent to 1 percent bariumhydroxide) was dissolved in the 9 percent sodium hydroxide mercerizingsolution prior to mercerization treatment of the pulp. The yield ofmercerized pulp product in this instance was 90.9 percent. This was anincrease of 3.8 percent of the control portion.

The third portion of pulp was mercerized in the same manner as the firstexcept that barium acetate (equivalent to l percent barium hydroxide)was dissolved in the 9 percent sodium hydroxide mercerizing solutionprior to mercerization of the pulp. The yield of mercerized product was92.6 percent. This was an increase of 5.7 percent over the controlportion.

While the principles of the invention have been described above inconnection with specific apparatus and applications, it is to beunderstood that this description is made only by way of example and notas a limitation on the scope of the invention.

We claim:

1. A process for producing a high yield of mercerized wood pulpcomprising: preparing an aqueous solution including a minor amount of abarium compound and a mercerizing concentration of alkali and treatingsaid wood pulp with said solution at a temperature of from about -60 C.

2. The process of claim 1 wherein the barium compound is selected fromthe group consisting of barium hydroxide, barium chloride, bariumacetate, barium sulfide and mixtures thereof.

3. The process of claim I wherein said solution contains between about0.10 percent and 3 percent by weight barium compound and between about 5percent and 18 percent by weight alkali.

4. The process of claim 1 wherein the temperature is from about 2540 C.

5. A process for preparing mercerized products containing a substantialamount of alkali-soluble short-chain polysaccharides comprising treatinga cellulosic material in a single step with an aqueous caustic solutioncontaining a minor amount of a ban'um compound and a mercerizingconcentration of alkali.

6. The process of claim 5 wherein said barium compound is selected fromthe group consisting of barium hydroxide, barium chloride, bariumacetate, barium sulfide and mixtures thereof.

7. The process of claim 5 wherein said solution comprises between about0.10 percent and 3 percent by weight barium hydroxide and between about5 percent and 18 percent by weight alkali.

8. The process of claim 7 wherein said cellulosic material is paperpulp.

9. The mercerized product prepared by the process of claim 5.

i t i i

2. The process of claim 1 wherein the barium compound is selected fromthe group consisting of barium hydroxide, barium chloride, bariumacetate, barium sulfide and mixtures thereof.
 3. The process of claim 1wherein said solution contains between about 0.10 and 3 percent byweight barium compound and between about 5 and 18 percent by weightalkali.
 4. The process of claim 1 wherein the temperature is from about25*-40* C.
 5. A process for preparing mercerized products containing asubstantial amount of alkali-soluble short-chain polysaccharidescomprising treating a cellulosic material in a single step with anaqueous caustic solution containing a minor amount of a barium compoundand a mercerizing concentration of alkali.
 6. The process of claim 5wherein said barium compound is selected from the group consisting ofbarium hydroxide, baRium chloride, barium acetate, barium sulfide andmixtures thereof.
 7. The process of claim 5 wherein said solutioncomprises between about 0.10 and 3 percent by weight barium hydroxideand between about 5 and 18 percent by weight alkali.
 8. The process ofclaim 7 wherein said cellulosic material is paper pulp.
 9. Themercerized product prepared by the process of claim 5.